Keep it running in a linear region, add some feedback around it to compensate, and there's no reason it shouldn't sound solid state.
There's a lot of cheaper guitar amps around that use a valve for marketting purposes. Its a simple cathode follower arrangement (often a 12AX7 or equivalent), and the overdrive sound is provided by some LEDs in the feedback loop of an op-amp. Lovely... NOT.

I'm working on a project to get the saturated-valve-output-stage sound from as small a box as possible, and will start a thread when I've got something to show for it.